• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.127-135
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• 2005

In order to analyze effects of strain rate on consolidation characteristics of Busan clay, a series of constant rate of strain (CRS) consolidation tests with different strain rate and incremental loading tests (ILT) were performed. From experimental test results on Busan clay, it was found that the preconsolidation pressure was dependent on the corresponding strain rate occurring during consolidation process. Also, consolidation curves normalized with respect to preconsolidation pressure gave a unique stress-strain curve. Coefficient of consolidation and permeability estimated from CRS test had a tendency to converge to a certain value at normally consolidated range regardless of strain rate. An increase in excess pore pressure was observed after the end of loading without change of total stress on the incremental loading test, which phenomenon is called Mandel-Cryer effect. It was also found that rapid generation of excess pore pressure took place due to collapse of soil structure as effective stress approached to preconsolidation pressure.

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.37-46
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• 2014

Geotechnical structures have been analyzed and constructed in various geometry conditions to maintain their stability in accordance with the characteristics of construction design. Shear strengths are generally obtained from triaxial test to apply to design analysis. Geotechnical structures under strip loading, such as earth dam, embankment, and retaining wall, have the strain in a direction, and plane strain condition. Thus, an approximate shear strengths should be applied for stability analysis suitable to ground condition. When applying shear strengths obtained from triaxial tests for slope stability analysis, the evaluation of it may underestimate the factor of safety because the implementation is not suitable for geometry condition. The paper compares shear strengths obtained from triaxial test and plane strain test based on various relative densities using weathered granite soils. Additionally, yield stress is determined by maximum axial strain 15% in triaxial test because of continuous kinematic hardening, but plane strain test can determine a failure point in critical state to evaluate the shear strengths of soils at the second plastic hardening step. This study proposes to perform an appropriate test for many geotechnical problems with plane strain condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1603-1611
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• 2004

The validity of 'modified overlay model' to describe the cyclic behavior of annealed 316L stainless steel at room temperature was investigated. Material parameters(~f$_{i}$, m$_{i}$b, η, E) fur the model were obtained through constant strain amplitude test. The strain amplitude dependency of elastic limit and cyclic hardening, which were the characteristics of this model, were considered. Eight subelements were used to describe the nonlinearity of the hysteresis loops. The calculated hysteresis curve in each condition (0.5％, 0.7％, 0.9％ train amplitude test) was very close to the experimental one. Two tests, incremental step test and 5-step test, ere performed to check the validity of 'modified overlay model'. The elastic limit was saturated to the one of the highest strain amplitudes of the block in the incremental step test, so it seemed to be Masing material at the stabilized block. Cyclic hardening was successfully described in the increasing sequence of the strain amplitude in 5-step test. But, the slight cyclic softening followed by higher strain amplitude would not be able to simulate by'modified overlay model'. However, the discrepancy induced was very small between the calculated hystereses and the experimental ones. In conclusion,'Modified overlay model'was proved to be appropriate in strain range of 0.35％~ 1.0％..0％.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• International Journal of Railway
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• v.8 no.2
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• pp.50-54
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• 2015

The primary function of the trackbed in a conventional railway track system is to decrease the stresses in the subgrade to be in an acceptable level. A properly designed trackbed layer performs this task adequately. Many design procedures have used assumed and/or are based on critical stiffness values of the layers obtained mostly in the field to calculate an appropriate thickness of the sublayers of the trackbed foundation. However, those stiffness values do not consider strain levels clearly and precisely in the layers. This study proposes a method of computation of stiffness that can handle with strain level in the layers of the trackbed foundation in order to provide properly selected design values of the stiffness of the layers. The shear modulus values are dependent on shear strain level so that the strain levels generated in the subgrade in the trackbed under wheel loading and below plate of Repeated Plate Bearing Test (RPBT) are investigated by finite element analysis program ABAQUS and PLAXIS programs. The strain levels generated in the subgrade from RPBT are compared to those values from RC (Resonant Column) test after some consideration of strain levels and stress consideration. For comparison of shear modulus G obtained from RC test and stiffness moduli $E_{v2}$ obtained from RPBT in the field, many numbers of mid-size RC tests in laboratory and RPBT in field were performed extensively. It was found in this study that there is a big difference in stiffness modulus when the converted $E_{v2}$ values were compared to those values of RC test. It is verified in this study that it is necessary to use precise and increased loading steps to construct nonlinear curves from RPBT in order to get correct $E_{v2}$ values in proper strain levels.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.377-382
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• 2004

The dynamic material characteristics on some mild steel sheets were observed. The dynamic tests were conducted on the ESH servo-hydraulic test machine. It was observed that the mechanical properties of mild steel are highly sensitive to the value of strain rate. The well known Cowper-Symonds constitutive equation was used to generalize the strain rate sensitivity effect. Modified constitutive equations were suggested to couple the strain hardening to the strain rate sensitivity. The dynamic stress-strain relationships for the mild steel sheets used in the present study were reasonably predicted using these modified constitutive equations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.154-158
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• 2002

The mechanical properties of Al 6061 excluded bar were deformed in high temperature with the variable deformation conditions and characterized by the tensile test. Three types of different strain rate were experimentally performed by using hydraulic press, crank press and hammer and two types of the nominal strain 0.5 and 0.8 were achieved. To decide optimum forging process, the relationship among the strain rate, strain and mechanical properties was explained by analyzing the microstructures of the forged and heat heated parts. The strength was deeply related with the strain rate due to the dynamic recrystallization (DRX) in hot forging, and the best forging condition was presented in Al 6061 alloy.

• Advanced Composite Materials
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• v.16 no.2
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• Computers and Concrete
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• v.22 no.6
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• pp.563-572
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• 2018

Uniaxial compressive strength test and uniaxial compression creep one were produced on four groups of twelve concrete specimens with different hole number by RLW-2000 rock triaxial rheology test system. The relationships between horizontal holes and instantaneous failure stress, the strain, and creep failure stress, the strain, and the relationships between stress level and instantaneous strain, creep strain were studied, and the relationship between horizontal holes and failure mode was determined. The results showed that: with horizontal hole number increasing, compressive strength of the specimens decreased whereas its peak strain increased, while both creep failure strength and its peak strain decreased. The relationships between horizontal holes and compressive strength of the specimens, the peak strain, were represented in quadratic polynomial, the relationships between horizontal holes and creep failure strength, the peak strain were represented in both linear and quadratic polynomial, respectively. Instantaneous strain decreased with stress level increasing, and the more holes in the blocks the less the damping of instantaneous strain were recorded. In the failure stress level, instantaneous strain reversally increased, creep strain showed three stages: decreasing, increasing, and sharp increasing; in same stress level, the less holes the less creep strain rate was recorded. The compressive-shear failure was produced along specimen diagonal line where the master surface of creep failure occurred, the more holes in a block, the higher chances of specimen failure and the more obvious master surface were.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.194-197
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• 2007

The dome stretching and tension test have been made to obtain a forming limit curve(FLC) for the copper alloy which is used for manufacturing the regenerative cooling chamber. For experimental survey of the forming limit curve, we have used in-plane tension specimen to obtain tension-compression strain state and also out of plane specimen to obtain tension-tension strain state through dome stretching test. All specimens are divided into longitudinal and radial direction specimens by the manufacturing method. The test results shows that in tension-tension region, copper alloy possesses a maximum major strain of 62.3% and maximum minor strain of 58.6%. In the tension-compression region, maximum major strain is 60.5% and maximum minor strain is 25.8%.